FBI TURMOIL ADDS CAUTION TO TWA CASE.

Byline: David Johnston The New York Times

In clean, brightly lighted laboratories at the J. Edgar Hoover Building, the scientific examination of mangled pieces of wreckage from TWA Flight 800 inches forward. Far from the grim recovery effort, away from the victims' grieving families, teams of white-coated chemists, metallurgists and explosives experts quietly scrape, swab and pick through the shattered debris flown from Long Island, N.Y.

If the atmosphere is antiseptic, forensic experts say the mood is tense, particularly since the scientists know that the Justice Department, and people around the world, are looking to them to make the call on whether the plane was brought down by a bomb. The experts stand over steaming test vats, glass beakers and carefully calibrated instruments in the search for an answer. So far, their findings have been agonizingly consistent: not a trace of an explosive chemical.

But the pressure from a world waiting for an explanation is not the only cause of anxiety within the cloistered world of the Federal Bureau of Investigation's crime lab. The lab's legendary reputation for scientific sleuthing has itself been under investigation. It is at the center of a Justice Department inquiry into its objectivity and methods.

FBI officials deny it, but several former and current law enforcement representatives suggested that a long-running internal inquiry at the lab by the Justice Department's inspector general is contributing to an atmosphere of caution about declaring the Trans World Airlines crash a criminal act.

Some officials said the caution has contributed to a decision by top FBI officials to wait for incontrovertible evidence before saying publicly what most of them acknowledge privately: that Flight 800 was deliberately downed by an explosive device. ``They know they're under the gun on this one,'' said one FBI veteran. ``No way can they make a mistake on TWA.''

But other FBI officials and forensics experts said that the crime lab cannot afford to speculate on such a high-profile case, and must be certain about the cause before the FBI formally takes over the case from the National Transportation Safety Board. These officials said the FBI was exercising an appropriate level of scientific discipline, waiting until its experts had hard proof before reaching a conclusion. And other FBI officers on Long Island note that only a small percentage of the wreckage has been pulled from the ocean and moved to Washington for testing.

The FBI's reluctance to reach firm conclusions more than two weeks after Flight 800 broke apart follows what has been an unusually turbulent period for the crime lab. It has a $63 million budget and more than 550 employees, among them experts in chemistry, toxicology, hair and fiber, fingerprints, ballistics, ink and paper - even people who specialize in tire and shoe tracks.

Until the TWA crash, the lab's explosive unit was criticized not for being slow to reach a conclusion, but for shooting from the hip. Much of the criticism has come from Frederic Whitehurst, a highly credentialed FBI chemist, whose complaints led to the internal inquiry.

Whitehurst, a veteran of 14 years who first complained to FBI officials in 1989, has said that FBI explosives experts and other analysts lacked necessary qualifications to make expert judgments, leaped to conclusions without sufficient scientific evidence and misinterpreted their findings.

``There was a quality assurance breakdown within the management of the lab and explosive unit in particular,'' said Stephen M. Kohn, a lawyer for Whitehurst, who was a chief chemist and the top explosives-residue expert until he was in effect demoted to a lesser job in the paint analysis unit in 1994. He has since been moved again, to a job involving environmental crimes.

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Photo: Wreckage from TWA Flight 800 is unloaded Friday at S hinnecock Coast Guard Station in Hampton, N.Y.

Associated Press